Recent studies have highlighted the possible role of intrauterine exposure to maternal diabetes in the pathogenesis of overweight, type 2 diabetes and cardiovascular disease. A hyperglycaemic intrauterine environment may also affect cognitive function, childhood growth and pubertal development in the offspring. During 1993-99 all pregnancies in women with pre-gestational type 1 diabetes were prospectively reported to a national registry in the Danish Diabetes Association. This nationwide registry contain detailed information of maternal demography, pregnancy outcome and diabetes status including glycated haemoglobin (HbA1c) in a prospective cohort of 900 women and their newborn offspring. These data are therefore ideal for a large-scale study on long-term effects of a diabetic intrauterine environment.